In chemical recovery furnaces, smelt is deposited on the inside surfaces of the primary air ducts. When solidified, the layers of smelt build up to form an increasingly serious obstruction to the primary air flowing through the duct to the combustion process in the furnace. At first when this problem arose, it was solved with a manually manipulated steam lance, or a blunt impact bar. From the beginning, this has not been a satisfactory way to remove smelt buildup. A structure which will actually scrape the smelt buildup from the walls of the air duct is desired. These past scrapers have had varying degrees of success, but there is still a problem. A scraping structure is needed which can be permanently mounted in the air ducts and actuated to carry out its scraping function by a mechanically and remotely controlled connection station.